Drilling Thru 12 Inch Block+Inner Wall

The wall is ceramic tile, drywall, foam, and then 12" concrete block (I can't detect any hollow). I have a 12" long masonry bit but the total wall is something like 18 inches!
Is there a way of detecting where the drill is located from the outside (after maxing the depth from the inside)?
I was wondering about studfinders that can detect live wires and metal studs or a non-contact voltage detector and connecting a live wire to the bit or rod...any thoughts on this?
Thanks!
Bob_V

Cut a metal hanger, sharpen the point and chuck it into your drill. Drill
the max depth with the masonry bit and then use the wire to complete the
hole.
A hanger will go through both wood and block. BTDT

d rod?
Silver solder won't hold up.
Start on the outside and drill a test hole to see if the block is hollow.
If it is, drill your outside hole and use a piece of wire to figure out how
far you are from the sides of the hollow space in the block. Then you sho
uld be able to use a tape measure to hit the same hollow from inside. The
holes won't be exactly opposite but probably close enough. You can make th
e outside hole a bit bigger to help. Then get that concrete patch in a cau
lk style tube to "grout" the hole after you run what ever it is you want to
run through it.

an't detect any hollow). I have a 12" long masonry bit but the total wall i
s something like 18 inches! Is there a way of detecting where the drill is
located from the outside (after maxing the depth from the inside)? I was wo
ndering about studfinders that can detect live wires and metal studs or a n
on-contact voltage detector and connecting a live wire to the bit or rod...
any thoughts on this? Thanks! Bob_V
An extension holder for the bit is not that expensive, assuming you have a
decent hardware store within 20 miles or so.

So If you are unlucky and hit a web you lack 6" of depth in the concrete
block; if not on a web, maybe 1 1/2". For that, you could take a steel
rod, shape the end some and bang away with a hammer. Ultimately, you'll
probably pop out a sizeable chunk.
As far as going from the other side, how accurately can you drill and
measure?

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